In recent years, a non-contact electrical power transmission system which transmits electrical power in a wireless manner without connecting the apparatuses by means of a cable has been developed. In the non-contact electrical power transmission system, electrical power supply efficiency changes depending on the distance between the electrical power transmission apparatus and the electrical power receiving apparatus in the non-contact electrical power transmission system or the surrounding environment. For this reason, in the non-contact electrical power transmission system, it is important to achieve high electrical power supply efficiency in any usage environment.
One of the contributing factors in a decline in electrical power supply efficiency is, for example, impedance mismatching between the electrical power transmission and receiving apparatuses in the non-contact electrical power transmission system. Impedance mismatching occurs due to changes in impedance of the antennas of the electrical power transmission and receiving apparatuses with the change in the distance between the electrical power transmission and receiving apparatuses or the surrounding environment when using the non-contact electrical power transmission system. Additionally, impedance matching between a power source apparatus generating electrical power in the electrical power transmission apparatus and a load part using electrical power in the electrical power receiving apparatus is not obtained. As a result, the electrical power is reflected, and the electrical power supply efficiency is declined.
As the related art for solving this problem, for example, Patent Literature (hereinafter, abbreviated to as PTL) 1 discloses a non-contact electrical power transmission apparatus which has an impedance variable circuit. In PTL 1, an electrical power transmission apparatus includes an A/C power source and an electrical power transmission antenna, and an electrical power receiving apparatus includes an electrical power receiving antenna, a load, and an impedance variable circuit. The impedance variable circuit adjusts impedance to suppress changes in impedance of a resonant system constituted by the electrical power transmission antenna, the electrical power receiving antenna, and the load. Accordingly, the technique of PTL 1 obtains impedance matching between the A/C power source and the resonant system, and maintains electrical power supply efficiency.